Mixed halide scintillators for radiation detection

ABSTRACT

Mixed halide scintillation materials of the general formula AB (1-y) M y X′ w X″ (3-w) , where 0≤y≤1, 0.05≤w≤1, A may be an alkali metal, B may be an alkali earth metal, and X′ and X″ may be two different halogen atoms, and of the general formula A (1-y) BM y X′ w X″ (3-w) , where 0≤y≤1, 0.05≤w≤1, A maybe an alkali metal, B may be an alkali earth metal, and X′ and X″ are two different halogen atoms. The scintillation materials of formula (1) include a divalent external activator, M, such as Eu 2+  or Yb 2+ . The scintillation materials of formula (2) include a monovalent external activator, M, such as Tl + , Na +  and In + .

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national phase application based onInternational Application No. PCT/US2015/029895, filed May 8, 2015, andclaims the benefit of U.S. Provisional Application, Ser. No. 61/990,541,filed May 8, 2014, entitled “MIXED HALIDE SCINTILLATORS FOR RADIATIONDETECTION,” the disclosure of which is incorporated herein by referencein its entirety.

FIELD OF THE INVENTION

The present invention is related to scintillation materials used todetect radiation such as X-rays, gamma rays, and thermal neutronradiation.

BACKGROUND

A scintillator is a material that can absorb high-energy particles andconvert these particles to multiple low-energy photons. Scintillationmaterials are scientifically and economically significant in conjunctionwith photodetectors to detect high-energy photons, electrons and otherparticles in various applications, which include medical imaging,geological exploration, homeland security, and high-energy physics. Inorder to maximize the scintillator's values in the applications,characteristics including high scintillation light yield, fastscintillation decay time and rise time, good energy resolution, highdegree of proportionality, proper emission wavelength, and good thermalresponse over a wide temperature range are desired. To these ends, it isimportant to obtain electron/hole traps and defect free scintillators.

Halide scintillators that contain a monovalent or a divalent externalactivator are a promising class of scintillators. Monovalent externalactivators include Tl⁺, Na⁺ and In⁺. For example, CsBa₂I₅ doped withTl⁺, Na⁺ and In⁺ scintillators are manufactured and used as gamma-raydetectors in “Scintillation Properties of CsBa₂I₅ Activated withMonovalent Ions Tl⁺, Na⁺ and In⁺,” by M. Gascón, et al., Journal ofLuminescence, 2014, 156, 63-68. Eu²⁺ and Yb²⁺ are examples of divalentexternal activators. Several Eu²⁺-doped halide scintillators showing ahigh light output and melting congruently, which allows thescintillators to be grown using the Bridgman-Stockbarger technique, havebeen described. For example, Eu²⁺-doped CsSrI₃ scintillators areprepared and their photophysical properties are disclosed in “CrystalGrowth and Characterization of CsSr_(1-x)Eu_(x)I₃ High Light YieldScintillators,” by K. Yang, et al., Rapid Research Letters, 2011, 5,43-45 and in “Optical and Scintillation Properties of Single CrystalCsSrl-xEuxI3,” by K. Yang, et al., Nuclear Science Symposium ConferenceRecord (NSS/MIC), 2010IEEE2010, 1603-1606. U.S. Patent Pub. No.2012/0273726 by M. Zhuravleva, et al. reported the scintillationproperties of CsSrBr₃ doped with Eu²⁺. Another example, “New SingleCrystal Scintillators, CsCaCI₃: Eu and CsCaI₃: Eu,” by M. Zhuravleva, etal., Journal of Crystal Growth, 2012, 352, 115-119, described thescintillation properties of CsCaI₃ and CsCaCI₃ doped with Eu²⁺.Scintillator crystals of CsBaI₃ doped with Eu²⁺ were found to haveexcellent scintillator properties as disclosed in “New PromisingScintillators for Gamma-Ray Spectroscopy: Cs(Ba,Sr)(Br,I)₃,” by U.Shirwadkar, et al., IEEE Nuclear Science Symposium Conference Record,2011, 1583-1585.

The use of mixed-halide scintillators, i.e., scintillators containingtwo or more different halide atoms, has been proposed as a means ofincreasing scintillator light output as shown in “ScintillationEfficiency Improvement by Mixed Crystal Use,” by A. V. Gektin, et al.,IEEE Transactions on Nuclear Science, 2014, 61, 262-270. Mixed-halidescintillators have been exemplified in limited contexts. For example,mixed-halide elpasolite scintillators of Cs₂NaYBr₃I₃ and Cs₂NaLaBr₃I₃doped with the trivalent activator Ce³⁺ are fabricated and their opticalproperties reported in “Two New Cerium-Doped Mixed-Anion ElpasoliteScintillators: Cs₂NaYBr₃I₃ and Cs₂NaLaBr₃I₃,” by H. Wei, et al., OpticalMaterials, 2014, 38, 154-160. Ce³⁺-based single crystal mixed-halidescintillators are reported in “The Scintillation Properties ofCeBr_(3-x)Cl_(x) Single Crystals,” by H. Wei, et al., Journal ofLuminescence, 2014, 156, 175-179. In another example, in “Scintillationand Optical Properties of BaBrI:Eu²⁺ and CsBa₂I₅:Eu²⁺ ,” IEEETransactions on Nuclear Science, 2011, 58, 3403-3410, G. Bizarri, et al.reported Eu²⁺-doped scintillators of BaBrI.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates differential scanning calorimetry thermograms for anexemplary CsSrBrI₂ (Eu 7%) scintillator, an exemplary CsSrClBr₂ (Eu 10%)scintillator, and an exemplary CsCaBrI₂ (Eu 7%) scintillator.

FIG. 2A illustrates the crystal growth of an exemplary CsSrBrI₂ (Eu 7%)scintillator in the ampoule.

FIG. 2B illustrates a bare crystal of an exemplary CsSrBrI₂ (Eu 7%)scintillator.

FIG. 2C illustrates a 5×5×5 mm³ polished sample of an exemplary CsSrBrI₂(Eu 7%) scintillator.

FIG. 3A illustrates the crystal growth of an exemplary CsCaBrI₂ (Eu 7%)scintillator in the ampoule.

FIG. 3B illustrates a bare crystal of an exemplary CsCaBrI₂ (Eu 7%)scintillator.

FIG. 3C illustrates an 8×8×20 mm³ polished sample of an exemplaryCsCaBrI₂ (Eu 7%) scintillator.

FIG. 4A illustrates the crystal growth of an exemplary CsSrClBr₂ (Eu10%) scintillator in an ampoule.

FIG. 4B illustrates a 6×5×13 mm³ polished sample of an exemplaryCsSrClBr₂ (Eu 10%) scintillator.

FIG. 5 illustrates the X-ray excited radioluminescence spectra of anexemplary CsSrBrI₂ (Eu 7%) scintillator, an exemplary CsCaBrI₂ (Eu 10%)scintillator, and an exemplary CsSrClBr₂ (Eu 10%) scintillator.

FIG. 6 illustrates the radioluminescence spectra of an exemplary KSrBrI₂(Eu 3%) scintillator.

FIG. 7 illustrates the radioluminescence spectra of an exemplaryRbSrBrI₂ (Eu 3%) scintillator.

FIG. 8 illustrates the radioluminescence spectra of an exemplaryCsSrBrI₂ (Yb 1%) scintillator.

FIG. 9 illustrates the radioluminescence spectra of an exemplaryCsSrBrI₂ (In 0.5%) scintillator.

FIG. 10 illustrates the scintillation decay time profile of an exemplaryCsSrBrI₂ (Eu 7%) scintillator, an exemplary CsCaBrI₂ (Eu 10%)scintillator, and an exemplary CsSrClBr₂ (Eu 10%) scintillator.

FIG. 11 illustrates the scintillation decay profile of an exemplaryKSrBrI₂ (Eu 3%) scintillator.

FIG. 12 illustrates the scintillation decay profile of an exemplaryRbSrBrI₂ (Eu 3%) scintillator.

FIG. 13 illustrates the scintillation decay profile of an exemplaryCsSrBrI₂ (Yb 1%) scintillator.

FIG. 14 illustrates the light yield as a function of europiumconcentration of an exemplary CsSrBrI₂ scintillator, an exemplaryCsSrClBr₂ scintillator, and an exemplary CsCaBrI₂ scintillator.

FIG. 15A illustrates the pulse height spectrum of an exemplary CsSrBrI₂(Eu 7%) scintillator.

FIG. 15B illustrates the pulse height spectrum of an exemplary CsCaBrI₂(Eu 7%) scintillator.

FIG. 15C illustrates the pulse height spectrum of an exemplary CsSrClBr₂(Eu 10%) scintillator.

FIG. 16 illustrates the pulse height spectrum of an exemplary KSrBrI₂(Eu 3%) scintillator.

FIG. 17 illustrates the pulse height spectrum of an exemplary RbSrBrI₂(Eu 3%) scintillator.

FIG. 18 illustrates the scintillation light yield per unit energy as afunction of deposited gamma-ray energy of an exemplary CsSrBrI₂ (Eu 7%)scintillator, an exemplary CsCaBrI₂ (Eu 7%) scintillator, and anexemplary CsSrClBr₂ (Eu 10%) scintillator.

FIG. 19 illustrates the photoluminescence spectra of an exemplaryCsSrBrI₂ (Eu 7%) scintillator.

FIG. 20 illustrates the transmission of exemplary CsSrI₃ (Eu 7%),CsSrBrI₂ (Eu 7%), and CsSrBr_(0.5)I_(2.5) (Eu 7%) scintillators.

FIG. 21 illustrates the light yield of exemplary CsSrI₃ (Eu 7%),CsSrBr_(0.25)I_(2.25) (Eu⁷%), CsSrBr_(0.5)I_(2.5) (Eu 7%),CsSrBr_(0.25)I_(2.25) (Eu 7%), and CsSrBrI₂ (Eu 7%) scintillators.

DETAILED DESCRIPTION

The present disclosure is directed to a group of newly discoveredmixed-halide scintillator compounds. These scintillators possessexcellent scintillator properties, such as high energy resolution andhigh light output.

Mixed-halide scintillators according to embodiments of the invention mayinclude two families with the following general exemplary formulas:AB_((1-y))M_(y)X′_(w)X″_((3-w))  (1)andA_((1-y))BM_(y)X′_(w)X″_((3-w))  (2)

-   -   where 0≤y≤1, and    -   0.05≤w≤1.

The scintillators of the formulas may include a monovalent or divalentexternal activator. In the formula (1), M may include a divalentexternal activator (such as Eu or Yb); A may include an alkali metal(such as Li, Na, K, Rb, Cs), indium (In), or any combination thereof; Bmay include an alkali earth metal (such as Mg, Ca, Sr, Ba, or anycombination thereof); and X′ and X″ are two different halogen atoms(such as F, Cl, Br, I) or any combination thereof.

The scintillators of formula (2) include a monovalent externalactivator. In the formula (2), M may include a monovalent externalactivator, such as In, Na, or Tl; A may include an alkali metal (such asLi, Na, K, Rb, Cs), indium (In), or any combination thereof; B mayinclude an alkali earth metal (such as Mg, Ca, Sr, Ba), or anycombination thereof; and X′ and X″ are two different halogen atoms (suchas F, Cl, Br, I), or any combination thereof.

The compounds of formulas (1) and (2) can form excellent scintillators.These new scintillators may be suitable for radiation detectionapplications including medical imaging, homeland security, high energyphysics experiments, and geophysical exploration. These scintillatorsare particularly notable for their high light output, excellent energyresolution, congruent melting, and practical crystal growth.

Embodiments of methods of making the mixed halide scintillators are nowdescribed. According to one embodiment, anhydrous high purity startingmaterials from Sigma-Aldrich were hand mixed in stoichiometric ratioaccording to the chemical formulas of the respective compounds andloaded into clean quartz ampoules. The mixing and loading were done in adry glove box with moisture and oxygen content of less than 0.01 ppm.

The starting materials were subsequently dried in the quartz ampouleunder 10⁻⁶ torr vacuum at 200° C. for 4 hours, cooled down to roomtemperature, and sealed inside of the quartz ampoule under vacuum with ahydrogen/oxygen torch. A single zone furnace may be used to melt andsynthesize compounds of formulas (1) and (2), but it shall beappreciated that other furnaces, including without limitation a two zonetransparent furnace and a three zone vertical Bridgman furnace, may beused.

In this embodiment, the melt and synthesis temperature was raised to 20°C. above the highest melting temperature of the starting materials used.This temperature was held for 7 hours and cooled down to roomtemperature in 7 hours. The ampoule was inverted and the procedure abovewas repeated to encourage complete mixing and reacting of all startingmaterials. This resulted in polycrystalline samples. The synthesistechniques including without limitation, Bridgman method, electronicdynamic gradient method, Czochralski method, micro-pulling down method,thin film deposition, melt-freezing, and ceramic hot pressing may beused to produce the final product in poly-crystal, single crystal, thinfilm and ceramic forms.

According to another embodiment, the starting material may be mixedusing a multiple ampoule alternating (“MAA”) mixing process. MAA mixingis a multiple melt-mixing process in which the ampoule's orientation ina vertical furnace is inverted one time, or several times, in order tofacilitate uniform mixing of all starting materials for chemicalreactions. MAA mixing provides for a more homogeneous distribution ofstarting materials and improved mixture transparency. The number ofinversions employed in an MAA mixing process may be determined by avariety of factors including, for example, the particular startingmaterials, intended chemical reactions, form of the resultant product,and temperature. Additional detail on multiple ampoule alternatingmixing methods is presented by Wei et al. in “Scintillation Propertiesof Cs₃LaCl₆: Ce³⁺ and Cs₃LaBr₆:Ce³⁺ ,” IEEE Transactions on NuclearScience, 2014, 61, 390-396, the disclosure of which is incorporatedherein by reference.

Exemplary mixed-halide scintillators according to the present disclosureinclude crystals of formulas (1) and (2). Scintillation properties ofseveral of these exemplary scintillators are presented in Table I below.

TABLE I Scintillation Properties of Exemplary Scintillators Energy LightResolution Yield Radioluminescence (at Scintillation Composition(ph/MeV) Peak (nm) 662 KeV) Decay (μs) CsSrBrI₂ 60,000 455 3.5% 0.7(~85%) (7% Eu) CsCaBrI₂ 50,000 462 5.0% 1.2 (~90%) (7% Eu) CsSrClBr₂35,000 445 5.0% 2.5 (~95%) (10% Eu) CsCaBrI₂ ~35,000 5.9% (3% Eu)CsSrBrCl₂ ~32,000 8.7% (10% Eu) CsSrICl₂ ~30,000 (10% Eu) CsSrClI₂~40,000 (7% Eu) KSrBrI₂ ~36,500 460 1.8 (Eu 3%) RbSrBrI₂ ~37,200 453 1.7(~68%) (Eu 3%) CsSrBrI₂ ~22,000 453 1.9 (~54%) (Yb 1%) CsSrBrI₂ ~4,000530 (In 0.5%)Differential Scanning Calorimetry of Exemplary Scintillators

The melting points and crystallization points for exemplaryscintillators were measured using a Setaram Labsys Evo DifferentialScanning calorimeter (DSC). Samples were heated and cooled at 5° K/minbetween 25° C. and 800° C. under flowing ultra-high purity argon gas.DSC data from several exemplary scintillators is presented in FIG. 1.

FIG. 1 presents DSC data measured for an exemplary CsSrBrI₂ scintillator(Eu 7%), an exemplary CsSrClBr₂ scintillator (Eu 10%), and an exemplaryCsCaBrI₂ scintillator (Eu 7%). As shown in this figure, the DSC curve ofthe CsSrBrI₂ (Eu 7%) scintillator indicates the melting temperature is611° C., the DSC curve of the CsSrClBr₂ (Eu 10%) scintillator indicatesthat the melting temperature is 752° C., and DSC curve of the CsCaBrI₂(Eu 7%) scintillator indicates that the melting temperature is 671° C.

Crystal Growth of Exemplary Scintillators

Crystal growth of an exemplary CsSrBrI₂ (Eu 7%) scintillator is shown inFIGS. 2A to 2C. In FIG. 2A the crystal growth of the CsSrBrI₂scintillator (Eu 7%) in the ampoule is shown. FIG. 2B illustrates a barecrystal of an exemplary CsSrBrI₂ scintillator (Eu 7%). FIG. 2Cillustrates a 5×5×5 mm³ polished sample of an exemplary CsSrBrI₂scintillator (Eu 7%).

FIGS. 3A to 3C show the crystal growth of an exemplary CsCaBrI₂ (Eu 7%)scintillator. In FIG. 3A the crystal growth of an exemplary CsCaBrI₂scintillator (Eu 7%) in the ampoule is shown. FIG. 3B illustrates a barecrystal of an exemplary CsCaBrI₂ scintillator. FIG. 3C illustrates an8×8×20 mm³ polished sample of an exemplary CsCaBrI₂ scintillator (Eu7%).

FIGS. 4A and 4B show the crystal growth of an exemplary CsSrClBr₂ (Eu10%) scintillator. FIG. 4A illustrates the crystal growth of anexemplary CsSrClBr₂ scintillator (Eu 10%) in an ampoule, and FIG. 4Billustrates a 6×5×13 mm³ polished sample of an exemplary CsSrClBr₂scintillator (Eu 10%).

Radioluminescence of Exemplary Scintillators

Radioluminescence spectra of exemplary scintillators were measured atroom temperature under continuous irradiation from an X-ray generatormodel CMX003 (at 35 kV and 0.1 mA). A model PI Acton Spectra Pro SP-2155monochromator was used to record the spectra. FIG. 5 illustrates theradioluminescence emission of several exemplary scintillators. Thesedata show a single peak emission attributed to the characteristicemission of Eu²⁺ 5d-4f transitions, which shows that Eu²⁺ enters thelattice in divalent form. The energy of Eu²⁺ 5d-4f excited states isdescribed by P. Dorenbos in “Energy of the First 4f²→4f⁶5 d Transitionof Eu²⁺ in Inorganic Compounds,” Journal of Luminescence, 2003, 104,239-260 and luminescence from this excited state is reported by D. H.Gahane, et al., in “Luminescence of Eu²⁺ in Some Iodides,” OpticalMaterials, 2009, 32, 18-21, and these disclosures are incorporatedherein by reference.

As shown in the radioluminescence spectra presented in FIG. 5, anexemplary CsSrBrI₂ scintillator (Eu 7%) has a single peak centered at455 nm; an exemplary CsCaBrI₂ (Eu 10%) scintillator has a single peakcentered at 462 nm; and an exemplary CsSrClBr₂ scintillator (Eu 10%) hasa single peak centered at 445 nm.

FIGS. 6 to 9 present the radioluminescence spectra of additionalexemplary scintillators. As shown in FIG. 6, an exemplary KSrBrI₂ (Eu3%) scintillator has a single peak centered at 460 nm. An exemplaryRbSrBrI₂ (Eu 3%) scintillator has a single peak centered at 453 nm, asshown in FIG. 7. FIG. 8 shows an exemplary CsSrBrI₂ (Yb 1%) scintillatorhaving a single peak centered at 453 nm. FIG. 9 shows an exemplaryCsSrBrI₂ (In 0.5%) scintillator having a single peak centered at 530 nm.

Scintillation Decay of Exemplary Scintillators

Scintillation decay time of exemplary scintillators was recorded using a¹³⁷Cs source and the time-correlated single photon counting techniquedescribed by L. M. Bollinger, et al., in “Measurement of Time Dependenceof Scintillation Intensity by a Delayed-Coincidence Method,” The Reviewof Scientific Instruments, 1961, 32, 1044-1050, and this disclosure isincorporated herein by reference. Scintillation decay profiles ofseveral exemplary scintillators are illustrated in FIGS. 10 to 13.

FIG. 10 shows the scintillation decay profile of an exemplary CsSrBrI₂scintillator (Eu 7%), which has a primary decay component of 0.77 μsthat accounts for ˜89% of the total light output and the remaining lightis collected over 3 μs; the scintillation decay profile of an exemplaryCsCaBrI₂ scintillator (Eu 10%), which shows a double exponential decayresponse where the primary decay component of 1.2 μs accounts for ˜82%of the total light output and the remaining light is collected over alonger component; and the scintillation decay profile of an exemplaryCsSrClBr₂ scintillator (Eu 10%), which shows a double exponential decayresponse where the primary component is 2.5 μs and a faster component of0.38 μs comprises about ˜5% of the total light output. The scintillationdecay curves presented in this figure were fitted with a two-componentexponential decay function.

Decay profiles of additional exemplary scintillators are presented inFIGS. 11 to 13. FIG. 11 shows the scintillation decay profile of anexemplary KSrBrI₂ (Eu 3%) scintillator, fitted with a one-componentexponential decay function. FIG. 12 shows the decay profile of anexemplary RbSrBrI₂ (Eu 3%) scintillator, fitted with a two-componentexponential decay function. FIG. 13 shows the decay profile of anexemplary CsSrBrI₂ (Yb 1%) scintillator, fitted with a two-componentexponential decay function.

Scintillation Light Yield of Exemplary Scintillators

Scintillation light yield of exemplary scintillators was measured usinga Hamamatsu 3177-50 or R6231-100 photomultiplier tube (“PMT”) andrecording the response to gamma rays (from, e.g., a ¹³⁷Cs (Cesium-137isotope) source). Mineral oil was used to protect the samplescintillator crystal from degradation, as well as to provide an opticalcoupling between the sample scintillator crystal and the PMT such thatscintillation light generated in the sample scintillator crystal wouldtransmit to the PMT for measurement. The number of photoelectrons wascalculated from the position of the 662 keV photopeak and the peak fromsingle photoelectrons. The photopeaks were fitted with a Gaussianfunction to determine the center of the peak. The conversion from thenumber of measured photoelectrons to the number of photons/MeV emittedby the scintillator, i.e., the scintillator's light yield, wasaccomplished by convolving the quantum efficiency of the PMT as afunction of wavelength (measured by Hamamatsu, the manufacturer of thePMT) with the X-ray excited emission spectrum of the sample. Ahemispherical dome of Spectralon was used to improve the scintillationlight collection into the PMT and a shaping time of 10 μs was used toensure the complete integration of the light pulse. For the energyresolution and γ-ray response of ¹³⁷Cs, ⁵⁷Co, ¹⁰⁹Cd, ¹³³Ba and ²⁴¹Am,the specimens were placed in a quartz container filled with mineral oilto protect them from moisture during the measurement.

FIG. 14 presents the light yield of exemplary scintillators as afunction of europium concentration. For exemplary CsSrBrI₂ and CsCaBrI₂scintillators, a europium concentration of 7% gave the highest lightyield, 60,000 and 50,000 photons/MeV, respectively, as shown in FIG. 14.For an exemplary CsSrClBr₂ scintillator, a europium concentration of 10%gave the highest light yield, 35,000 photons/MeV.

The pulse height spectra of exemplary scintillators are shown in FIGS.15 to 17. The full-energy peak (photopeak) is fit by Gaussian functionin FIGS. 15A to 15C. In FIG. 15A, the pulse height spectrum of anexemplary CsSrBrI₂ scintillator (Eu 7%) crystal (crystal dimensions:4×2×2 mm³) under ¹³⁷Cs excitation is shown, and exhibits a light yieldof 60,000 photons/MeV and energy resolution of 3.5% at 662 KeV. In FIG.15B, the pulse height spectrum of an exemplary CsCaBrI₂ scintillator (Eu7%) crystal (crystal dimensions: 8×8×20 mm³) under ¹³⁷Cs excitation isshown, and exhibits a light yield of 50,000 photons/MeV and energyresolution of 5.0% at 662 KeV. In FIG. 15C, the pulse height spectrum ofan exemplary CsSrClBr₂ scintillator (Eu 10%) crystal (crystaldimensions: 4×2×2 mm³) under ¹³⁷Cs excitation is shown, and exhibits alight yield of 35,000 photons/MeV and energy resolution of 5.0% at 662KeV.

FIGS. 16 and 17 illustrate pulse height spectra of additional exemplaryscintillators, measured under ¹³⁷Cs excitation. In FIG. 16, the pulseheight spectrum of an exemplary KSrBrI₂ (Eu 3%) scintillator is shown,which exhibits a light yield of 36,500 photons/MeV. The pulse heightspectrum of an exemplary RbSrBrI₂ (Eu 3%) scintillator is presented inFIG. 17, and the exemplary RbSrBrI₂ (Eu 3%) scintillator exhibits alight yield of 37,200 photons/MeV.

FIG. 18 presents the scintillation light yield per unit energy as afunction of deposited γ-ray energy for several exemplary scintillatorcrystals. These data were obtained by irradiating exemplary scintillatorcrystals (crystal dimensions: 4×3×3 mm³) with γ-ray excitation energiesranging from 14 to 662 KeV.

As shown in FIG. 18, an exemplary CsSrBrI₂ scintillator (Eu 7%) exhibitsa proportional response from 20 to 662 keV and decreases by ˜6% at 14keV. Exemplary CsCaBrI₂ (Eu 7%) and CsSrClBr₂ (Eu 10%) scintillatorsbegin to exhibit non-proportionality at higher energies. Notably, theresponse curves of the exemplary mixed-halide scintillators lack thewell-known “halide hump”, i.e., the often-observed increase in lightyield at intermediate energies as described by S. A. Payne, et al., in“Nonproportionality of Scintillator Detectors: Theory and Experiment,”IEEE Transactions on Nuclear Science, 2009, 56, 2506-2512 as well as in“Scintillator Light Yield Nonproportionality: Calculating PhotonResponse Using Measured Electron Response,” IEEE Transactions on NuclearScience, 1997, 44, 509-516, by B. D. Rooney et al., and the disclosureof each is incorporated herein by reference. Instead, the responsecurves of the exemplary scintillators are similar to the responsecommonly observed for oxide scintillators in which the light yield isconstant for high and intermediate energies and then decreasesmonotonically at low energies.

Photoluminescence of Exemplary Scintillators

FIG. 19 presents the photoluminescence spectral features of an exemplaryCsSrBrI₂ scintillator (Eu 7%). These data were acquired using a HitachiFluorescence Spectrophotometer equipped with a Xenon lamp at roomtemperature. The spectral features illustrated in FIG. 19 involve 4f-5dexcited states and are characteristic of divalent europium luminescence.

Partial Halide Substitution

Partial substitution of the halide components of formulas (1) and (2)may improve scintillator performance. For example, FIG. 20 illustratesthe effect of partial halide substitution on the transmission ofexemplary CsSrI₃ (Eu 7%), CsSrBrI₂ (Eu 7%), and CsSrBr_(0.5)I_(2.5) (Eu7%) scintillators. The samples of these exemplary scintillators used tomeasure this data were grown by the Bridgman technique with MAA mixingto 3 mm in thickness. A shown in FIG. 20, the transmission of theexemplary CsSrI₃ (Eu 7%) scintillator was improved by approximately 35%by the 33% iodide for bromide halide substitution in the exemplaryCsSrBrI₂ (Eu 7%) scintillator, and by approximately 65% by the 16.6%iodide for bromide halide substitution in the exemplaryCsSrBr_(0.5)I_(2.5) (Eu 7%) scintillator.

The effect of partial halide substitution on light yield is illustratedin FIG. 21. Samples of exemplary CsSrI₃ (Eu 7%), CsSrBr_(0.25)I_(2.75)(Eu 7%), CsSrBr_(0.5)I_(2.5) (Eu 7%), CsSrBr_(0.75)I_(2.25) (Eu⁷%), andCsSrBrI₂ (Eu 7%) scintillators were melt-freeze synthesized with MAAmixing. As shown in this figure, the light yield of an exemplary CsSrI₃(Eu 7%) scintillator was increased by substituting bromide for iodide,and the maximum light yield was obtained at 8.33% iodide for bromidesubstitution.

It shall be appreciated that the disclosure may be not limited to thedescribed embodiments, and that any number of scenarios and embodimentsin which conflicting appointments exist may be resolved.

Although the disclosure has been described with reference to severalexemplary embodiments, it shall be understood that the words that havebeen used are words of description and illustration, rather than wordsof limitation. Changes may be made within the purview of the appendedclaims, as presently stated and as amended, without departing from thescope and spirit of the disclosure in its aspects. Although thedisclosure has been described with reference to particular examples,means, and embodiments, the disclosure may be not intended to be limitedto the particulars disclosed; rather the disclosure extends to allfunctionally equivalent structures, methods, and uses such as are withinthe scope of the appended claims.

The illustrations of the examples and embodiments described herein areintended to provide a general understanding of the various embodiments,and many other examples and embodiments may be apparent to those ofskill in the art upon reviewing the disclosure. Other embodiments may beutilized and derived from the disclosure, such that structural andlogical substitutions and changes may be made without departing from thescope of the disclosure. Additionally, the illustrations are merelyrepresentational and may not be drawn to scale. Certain proportionswithin the illustrations may be exaggerated, while other proportions maybe minimized. Accordingly, the disclosure and the figures are to beregarded as illustrative rather than restrictive.

One or more examples or embodiments of the disclosure may be referred toherein, individually and/or collectively, by the term “disclosure”merely for convenience and without intending to voluntarily limit thescope of this application to any particular disclosure or inventiveconcept. Moreover, although specific examples and embodiments have beenillustrated and described herein, it should be appreciated that anysubsequent arrangement designed to achieve the same or similar purposemay be substituted for the specific examples or embodiments shown. Thisdisclosure may be intended to cover any and all subsequent adaptationsor variations of various examples and embodiments. Combinations of theabove examples and embodiments, and other examples and embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

In addition, in the foregoing Detailed Description, various features maybe grouped together or described in a single embodiment for the purposeof streamlining the disclosure. This disclosure may be not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter may bedirected to less than all of the features of any of the disclosedembodiments. Thus, the following claims are incorporated into theDetailed Description, with each claim standing on its own as definingseparately claimed subject matter.

The above disclosed subject matter shall be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments which fall within thetrue spirit and scope of the present disclosure. Thus, to the maximumextent allowed by law, the scope of the present disclosure may be to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

We claim:
 1. A scintillator comprising a chemical compound having thechemical formulaA_((1-y))BM_(y)X′_(w)X″_((3-w)), wherein 0≤y≤1, 0.05≤w≤1, A is one ofLi, Na, K, Rb, Cs, In or any combination thereof, B is Mg, Ca, Sr, Ba orany combination thereof, M is In, Na or Tl, and X′ is one of F, Cl, Br,I or any combination thereof, and X″ is different from X′ and is one ofF, Cl, Br, and I or any combination thereof.
 2. The scintillator ofclaim 1, wherein 0≤y≤0.15.
 3. The scintillator of claim 1, wherein A isCs.